The American College of Sports Medicine and the American Heart Association jointly updated physical activity recommendations based on the most relevant science that links exercise to improved health and wellness. Both organizations' suggestions now focus on 30 minutes of moderate-intensity daily physical activity, five days a week. How do you know if you're pushing along at a moderate, versus a slightly, intensity? The easiest way is to monitor your personal Rate of Perceived Exertion, or RPE. Your RPE during any sort of exercise – from walking and biking to skating and even karate class -- can mean the difference between blasting hundreds of calories or cheating yourself out of results.

RPE corresponds directly to your heart rate during exercise, so ask yourself several times per workout which number from 1 to 10 below corresponds with how you're feeling. After you monitor your own RPE for two weeks or so, RPE comes naturally, no matter where or how you're exercising. For example:

RPE Scale: How to Start Tuning In

1. Sit still, quiet reading
2. Light effort, strolling
3. Moderate walking, warm-up and cool-down levels
4. Moderate plus, like walking 4 mph on a flat track or hiking a gentle hill
5. Moderately intense; walking fast enough to almost jog 5 mph
6. Intense, hiking up a steeply vertical hill and feeling breathless
7. More intense, running about 7 mph or taking an indoor cycling class
8. Fast work, like running in deep sand or power jumps over cones, or hurdling at top speeds
9. Nearly too high, definitely uncomfortable and gasping for breath
10. Exertion is way too high, heart is thumping and muscles are on fire; decrease intensity

If all of this is just too much to remember, try the instant and easy Talk Test: How do you know when you're overdoing it while exercising? Say the Pledge of Allegiance out loud. If it's too tough to voice those familiar words, you're probably pushing yourself too hard. And while your running shoes or yoga pass wasn't exactly cheapo, The Talk Test is free and requires no special training. Just be sure to say the words out loud, says ACSM. After all, you want to keep up the exercise habit, so progress in moderation and within a healthy RPE.

To start training at fat-blitzing intensities, experiment with a wide range of workouts.